Art of light-sensitive photographic materials



( Patented lillar. 2 1926.

UNITED STATES PATENT OFFICE.

SAMUEL E. SHEPIPARD, O1 ROCHESTER, NEW YORK, ASSIGNOR TO EASTMAN KODAK COMPANY, OF ROCHESTER, NEW -YORK, A CORPORATION OF NEW YORK.

ART OF LIGHT-SENSITIVE. PHOTOGRAPHIC MATERIALS.

No Drawing.

To all whom it may concern:

Be it known that I, SAMUEL E. SHEPPARD, a subject of the King of Great Britain, residing at Rochester, in the county of Monroe and State of New York, have invented certain new and useful Improvements in Art of Light-Sensitive Photographic Materials, of which the .following is a full, clear, and exact specification.

This invention relates to the art of photographic materials.

One object of the invention is to provide photographic sensitizing materials capable of greatly increasing the light sensitiveness of photographic emulsions, especially of the developing-out type, even when incorporated therein in very small amounts. Another object is to provide such materials in a concentrated and highly purified condition; so that they will not impair or harmfully dilute the emulsions in which they are used. A still further object is to provide processesfor obtaining said materials in said desirable condition.

Another object of the invention is to provide photographic emulsions, especially developing-out emulsions, having new and improved properties because of the use or presence therein of my independent sensitizing materials. Still another object of my in-' vention is to provide a process in which my said sensitizing materials are used to 1mprove photographic emulsions, especially developing-out emulsions, as regards light sen sitiveness, by which term I'include their ability to give the earliest visible impression or image with the minimum exposure or their ability to giye density after a given exposure or both, the usual photographic fluid treatments being used in preparing such impression or image.

A further object of the invention is to provide colloid products, such as treated gelatin, the usefulness of which for forming light sensitive photographic emulsions, especially developing-out emulsions, is greatly increased and controlled by my said sensitizing material incorporated therewith. Another object of the invention is to provide corresponding processes for makingsaid intermediate colloid products.

Other objects are,-to increase the sensitiveness of photographic emulsions, partic- 'ularly developing-out ones, while wholly or partially dispensing with expensive or long 1924. Serial No. 71e,41o.

and uncertain so-called ripening methods: to enable the use of a type of gelatin having desirable physical qualities in making. such a photographic emulsion of greater light sehsitiveness-than that normally obtainable with said gelatin; to obtain more stable emulsions through the purity of the ingredients; to increase the llght-sensitirven-ess of photographic emulsions, particularly develop ng-out ones, the grain characteristics of whlch have already been determined; to increase the general light-sensitiveness of such photographic emulsions throughout the spectral ranges to which they are normally sensitive; to make such photographic emulsions of standard light-sensitive characteristies with gelatins which normally do not produce emulsions having such characteristics; to, make, as intermediates in the manufacture of photographic emulsions, gelatins of standard light-sensitiveness giving power out of gelatins which do not normally have the power of giving such standard sensitive ness to emulsions, such as developing-out ones, made from them. Further ob ects will hereinafter appear.

I have found photographic sensitizing materials, very small amounts of which greatly increase the light-sensitiveness of photographic emulsions, such as those of the developing-out gelatino-silver-halid type for example. These materials I am able to prepare in especially concentrated and purified forms, so that when incorporated in 'such emulsions or gelatins for such emulsions, they produce their sensitivity-increasing action without harmfully diluting said emul- I sions or gelatin or impairing the physical properties and purity of them. Conseguently my sensitizing materials supply sa e, dependable, and practically independent means for controlling the properties of photographic emulsions in addition to the customaryexpedients. The increases in sensitiveness of developing-out emulsions appear upon the usual developing, fixing, washing, and drying operations. Any customary developer, like the usual pyro or metolhydrochinon alkaline developers, are suitable for example.

The active sensitizing body or bodies in my sensitizing materials originate biochemically in both plants and animals. It is found for instance in especially useful quantities in the sterol-containing extracts or cereal preparation, such as wheat, bran, rice hulls, peas, and beans. Of course, hides, bones, cereal grains and leguminous plant seeds, are only mentioned as illustrative of the many animal and vegetable organic tissues from which my sensitizing materials may bev prepared. 0

Different sources vary in the extent to which they contain sensitizing material; but

their-suitability can readily be determined by a simple test. -A small sample of the source in question can be extracted by,v a

method selected from the examples hereinafter given and the extract added to an emulsion such as one hereinafter described. If the sample sensitizing material causes a good increase in the light-sensitiveness of the emulsion, then the tested source can the bulky ones, pair or dilute photographic emulsions.

all be usefully extracted. This extraction of a sample and trial in a known emulsion provides a ready test for raw-material; but the preferred sources listed hereinabove are in general reliable sources when a test is dispensed with. It is preferable to use sources which have not been submitted to excessive oxidizing action, which tends to destroy the sensitizing power of the material.

In pre aring my sensitizing material, I free it i om certain of its originally or normally associated impurities, especially and those which might imenerally speaking the preferred prepara; tion of the material rids it of impurities insoluble in alcohol or those insoluble in li ht petroleum products such as ligroin. These are typical of the many organic solvents of my sensitizing compound which may be employed. Then some of the solvent is to enter emulsion, one is selected which is substantially free from injurious action on the emulsion, alcohol being particularly good in this respect. My preferred preparation likewise frees the material from mineral compounds.

I find upon separating the principal impurities from my sensitizing compounds that the resulting materials prove to be in most cases sterol-containing fractions. Such a useful sensitizing sterol extract is, or-example, one substantially all soluble in alcohol or ligroin. In general" these fractions are substantially free from water-insoluble impurities as well as free from at least art of the water-soluble but alcoholinsolu 1e or ligroin-insoiubleimpurities.

The purified sensitizing compounds or bodies in dry form and paste form and in the form of solutions are capable of increasing the sensitiveness of hotographic emulsions, when incorporated therein and so the term sensitizing material applies to any one of these forms.

While my invention is of wide utility in this art, it svespecially useful in connection with gelatino-silver-halid emulsions, such, for example, as developing-out emulsions employed on negative or positive films,

plates, papers, etc. The ammonia or alkame tge of such emulsions respond especially rea 'lytomy sensitizer. I shall, therefore, describe certain illustrative embodiments of my invention in connection with such emulsion's; but it will be understood. that my invention is not restricted to these examples but can be embodied in many other species.

I shall first give examples of the preparation of my sensitizing material from animal sources. An inexpensive source of this kind is found in the gelatin industry, especially in such by or waste products as the deliming solutions. Stock, which has been limed in the way that is customary in manufacturing gelatin, is delimed in dilute acid. Any of the customary deliming expedients may be used. I find it convenient, for example, to agitate limed hide-stock in one per cent hydrochloric acid at a temperature of about 70 F. until a thick piece of the stock, when cut across, shows itself slightly acid to litmus at the inner parts of the surfaces of the cut. The deliming solution, which is used in a large enough amount to cover the stock, isthen drawn ofi.

The dqliming solution is next concentrated, preferably at reduced pressure, say under 24 inches of vacuum at 170 F. The extent of concentration can vary widely according to the amount of material in the deliming solution before evaporation. Concentration to one forty-fourth of its original amount is a typical operation. It is convenient to do this in an evaporator of the climbing film. type lined with block tin, but, of course, this is not essential.

The concentrate, which may contain some suspended matter without harm, is boiled until a coagulum or precipitate is formed. The coagulum, which is chiefly albuminous, carries with it my sensitizing material which adheres to it. Any convenient way of separating the coa lumfrom the liquid may be employed; or instance, it may settle and the liquid be decanted off or it can be filtered out or centrifuged off. It can be washed with water but this is not essential.

In order to facilitate the extraction of the sensitizing material, the coagulum is preferably dried and ground. The drying is conveniently done in a steam heated oven at 200 F. and the comminuting done in a used can vary considerabl- For exam le,

for each 10 gallons (or 45'. liters) of dellming solution originally taken, there may be used on the resulting powder from 200 to 250 cc. (or 3,400 to 4,250 mins.) of ethyl alcohol. The alcoholic extract thus produced containssterols and strong sensitizing material, as do also the dry residue obtained by evaporating it.

In still another example of my invention I may again start with a deiiming solution as indicated in the first example. In this I form an inorganic precipitate to which the sensitizing compounds adhere. For instance, I add three-tenths of a pound (or four ounces 350 grains) of potassium alum to each ten allons of the deliming solution.

' The liquid 1s then brought nearly to boiling and about one-tenth of a pound (or one ounce 260 grains) of sodium hydroxide added. The amount of sodium hydroxide necessary to give the desired precipitate of aluminum hydroxide varies, of course, with the original acidity of the deliming solution. It can conveniently be added until the pH value is 8 as shown by phenol red, a well known indicator. s

The recipitate is allowed to settle, say overnigli decantation. Of course, filtration, centrifuging or other method can be used. The .aluminous pulp or precipitate thus obtained is dried, say at about 200 F; It is then ground to. pass a screen mesh of 40 to to the inch. Finally the ground powder is extracted, say with about 500 cc. (or 8,500 mins.) of ethyl alcohol for each 100. grams or 1,540 grains) of powdered precipitate. The extraction should take place without prolonged storage of the precipitate after it is owdered because the sensitizing material 1n the .powder becomes noticeably less upon standing, probably due to its oxidation into non-sensitizing compounds by air to which it is highly ex osed through the large aggregate surface 0 the powder. The extraction is conveniently done in a Soxhlet type of extractor and the resulting alcoholic solution, which contains sterols, is a strong sensitizing material, as is also the dry residue obtained therefrom upon evaporation." Alcohol in the above examples takes up not only the ,active sensitizing bodies but a little impurity also. Thus is clearly shown upon evaporating a sample of the. alcoholic extract to dryness;

the resulting solids being very small, yet ground in water, allowed to ferment for.

t and separated from the liquid by the meagre residue containing non-sensitizing substances. I have found that ligroin 'or a similar volatile petroleum solvent will take up substantially all the sensitizing material and still leave behind some non-sensitizing material which the alcohol had dissolved. Therefore, when I use ligroin as the extracting solvent, Iseparate in effect the sensitizing material from the alcohol-impurities as well as from the ligroin-insoluble impurities. For this purpose petroleum ether boiling between 40 -90 C. is useful but the ligroin fraction boiling between 40 and 60 C. is better. It may be substituted for the alcohol in the above examples, using about 100 cc. (or 1,700 mins.) for each 100 grams (or 1,540 grains) of dried pulp. It gives likewise a strong sensitizing material. Both the alcoholic extracts and the ligroin extracts contain sterols but are remarkably free from nitrogenous and min eral impurities and fogging agents. Since alcoholic extracts enter most emulsions better than ligroin solutions, the latter are preferably evaporated to dryness and the residue taken up in alcohol, say about 500 cc. (or 8,500 mins.) for each 100 cc. (or 1,700 mins.) of ligroin solution that was evaporated. Alcohol is an excellent spreading agent for the sensitizing bodies.

While I prefer to dry the precipitates and grind them in the above examples, they can, of course, be collected, and extracted with alcohol while still wet; but the extraction is not as quick or thorough as in the above described powdering methods.

In the next example there will be described the preparation'of my sensitizing material from vegetable sources. Wheat grains, corn, beans, peas, unhulled rice, wheat bran, mustard seeds, and rice hulls are a few illustrations of the types available. Mustard seed is the most fruitful source. "They are preferably comminuted and then extracted. For instance, lima beans are first ground to a coarse fiour,suific iently fine to expose a large aggregate surface to the extracting liquid. This flour, without being stored long enough to have its sensitizing material badly oxidized by the air, or volatilized, is extracted with ligroin boiling between 40 and 60 C. in a Soxhlet type of extractor. until the operation is completed say for about 5' or 6 hours; although a longer time-does no harm. For each kilogram (or 15,400 grains) of bean flour it is convenient to use 3 A), liters (or 56,600 mins.) of ligroin. The resulting extract is strong in sensitizing material. It is preferably evaporated to dryness .and the residue taken up in alcohol, say 1 liter (or 17,000 mins.) for each 3 liters (or 56,600 mins.) of the original ligroin extract.

Mustard seed, for another illustration, is

overnight, or say 12 hours, at room temperature. Then the mash is extracted, say by shaking with ligroin. I

This solution is a strong sensitizing material but can be concentrated and purified still further, if saponifiable oils be present in troublesome amounts. To remove 'such oils there is added to each liter of the final alcoholic extract, about 300 cc. (or 5,100 mins.) of the alcoholic extract from 7 grams (or 108 grains) of sodium hydroxide. Of course, the strength of this saponifying alkaline,s0luti0n can vary and equivalent solutions, like alcoholic potassium hydroxidebe substituted. The mixture is boiled in a paratus having a reflux condenser, until t e oils are saponified. The solution is then evaporated to dryness and the residue taken up in sufiicient water for that purpose. Ligroin or related petroleum ether is added with shaking. The sensitizing material enters the ligroin while the saponified oils and any liberated glycerine stay in the water. The ligroin extract is then separated out. It is convenient to use 660 cc. (or 11,220 mins.) of ligroin in this extraction for each liter (or 17,000 mins.). of alcoholic extract subjected to the saponification treatment. The ligroin is next eva orated off and the residue taken u in alco 01, 330 cc.

(or 5,610 mins.) for eac 66000. (or 11,220 mins.) of the ligroin from which the residue came. The finished alcoholic extract, which is likewise the sterol fraction from the beans, is a very powerful sensitizing material, purified from fogging agentsand from easy or oily impurities. It is likewise su stantially free from nitrogenous and. mineral compounds.

The final alcoholic sterol extracts containing the sensitizing compounds, such as the extracts described above from animal and vegetable sources are very useful but can be purified or concentrated evenfurthe'r by removing the" sterols, either wholly 'or partially. The sterols are substantially harmless to emulsions but are by themselves practically free from sensitizing actions,- consequently their separation is useful. This can be done, for example, by evaporating the sterol-containing fraction to dryness, taking up the dried residue in just enough warm I i but not boiling ethyl alcohol, say at 70 to 80 C., to dissolve it, cooling until sterol crystals form, removing said crystals, as by filtering, washing the crystals with a little ligroin, adding the wash liquid to the liquid from Which the crystals came, and finall concentrating the combined liquids pre erably under less than atmospheric ressure, by evaporation. Or the .combine liquids can be evaporated to dryness and the residue containing the sensitizing compounds dissolved in alcohol. If this first removal is insuflicient the process can be repeated.

aqueous ingredients).

My concentrated and purified sensitizing material whether in the form of a solution, a solidor a paste is very powerful. Important and useful increasesin light-sensitiveness of emulsions even occur when the actual sensitizing compounds or bodies in the sensitizing material are of the order of a' fifty-thousandth to a four hundred-thousandth of the weight ofthe emulsion in which they are incorporated. Of course, the sensitizing bodies can be incorporated in still lar er proportions but these minute amounts illustrate their. ower. Too much sensitizer tends to pro uce fog in some emulsions of the developing-out type. An excess should, therefore, be avoided. Usually the solids in the added extract in its purified form are less than one ten-thousandth of the weight of the emulsion (non- My sensitizing material is concentrated and free from bulky and harmful impurities, with which it was originally or normally associated. 'In other words the active sensitizing bodies are in general more concentrated and purer in my material than in the sources from which they are derived. This makes it especially useful without either 'diluting them to an und sirable extent or introducing fogging or ther harmful impurities. Stated in another way it increases their light-sensitiveness without deteriorating their other qualities, such as setting ability, melting point, viscosity, and grain-characteristics. It enables me to establish a ratio of sensitizing material to silver halid in the emulsions which is independent of the ratioof gelatin to silver halid.

The sensitizing bodies in my material appear to be not truly soluble in water but to form' colloidal solutions therein. Its solutions in alcohol and ligroin are true ones. My sensitizing material has a very useful stability provided excessive exposure to oxidizing influences is not allowed. It is generallyv neither markedly acid nor alkaline although it withstands dilute acid and alkalis and can be used when such are present in the emulsions. Since it is substantially without fogging action on emulsions when used in the proper amount for sensitizing themit yields emulsions of surprising stability when their sensitiveness is'considered, fogging being long delayed. I classify the material as biochemical or organic in distinction from inorganic materials such as ammonia and 'silver nitrate for example. The alcoholic solutions are, of course, protected from harmful bacterial action, the alcohol being a preservative. I

My sensitizing material acts as a so-called chemical sensitizer instead of an optical emulsions in which it is incorporated,that is to light of substantially the same wave lengths as those tof which the emulsion would be sensitive without the incorporation of my material; instead of merely increasing the sensitiveness tosome narrow group of wave lengths Unlike dyes the sensitiveness is increased throughout the normal spectral range of emulsion instead at only those spectral points corresponding to the spectral absorption of the sensitizing mater1al My material is effective in increasing the general light-sensitiveness oforthoc-hromatic, panchromatic, X-ray, and all special emulsions, as well as the ordinary or noncolor sensitized ones. It can be added with dyes or before or after them. It is nearly colorless itself. It is preferably added separately or independently of the sensitizing dye, generally but not necessarily before any dye. It is especially efiective in emulsions having, at least slight, alkalinity.

My sensitizing material may be used in many ways. Broadly it may be incorporated in emulsions or in colloids for' emulsions or both. It can also enter the emulsion mixed with other ingredients thereof whether organic or inorganic. It gives added light-sensitiveness to various emulsions having different speeds and'other distinctive characteristics. While it may be added at different stages of emulsion manufacture, nevertheless, it can be very conveniently mixed into the emulsion when the latter is otherwise complete ready for coating. Since its action is immediate when incorporated, the coating need be delayed only long enough to mix in the sensitizing material. With the grain characteristics,

such as size distribution etc. already determined, and the other hysical and photographic properties of t e emulsion already taken care ofat this stage, I can practically independently increase its light-sensitiveness without impairing said other properties by adding my concentrated purified sensitizing material.

As will be clear to those skilled in this art, the proportion of sensitizing material added tothe emulsions will vary according to the concentration of the sensitizing material and according to the increase in lightsensitiveness which is desired. The alcoholic extracts hereinabove described can be added, as a basis for trial, in the proportion of from 10 to 25 parts of extract to 1000 parts by volume of the emulsion. This is of the order of magnitude of 2 per cent.

mixing in my sensitizing material, the probelow a required manufacturing standa-rd of light-sensitiveness, although they may be I otherwise satisfactory, their sensitiveness can readily be brought up to standard by portion varying with the increase necessary. to produce a uniform product. Emulsions having almost no practical light-sensitiveness but having enough other desirable qualities can be made usefully light-sensi t1ve by my material. Thus the latter is useful in connection with emulsions having good initial light-sentiven'ess and those having almost no initial sensitiveness. The increase in sensitiveness can be effected in one step by thoroughly stirring all of the sensitizmg material into the emulsion at one time; or it may be incorporated part at a time'in successive steps.

' The following example illustrates how light sensitive photographic emulsion may 'to the salt solution.

Of course, larger proportions can be used,

provided harmful dilution is avoided; smaller amounts can be used for slight increases in sensitiveness and more concentrated extracts can be employed, or even the dried residues therefrom.

Where different batches of emulsion fall ample.

be prepared and improved by the aid of my sensitizing material. Of course, my invention is not restricted to this illustration but is applicable in the cases of the very large number of widely different emulsions in this 'art. The emulsion forming operations hereinafter described are along the lines of known practice, see for instance Die Photographie mit Bromsilber Gelatine by J. M. Eder, published in Halle, Germany, in 1903 by Wilhelm'Knapp as Part III of Eders Ausfiihrliches Handbuch der Photographie.

The two following solutions are made the parts being by weight:

A 900 parts of silver nitrate in 9, 200 parts of water.

690 parts of potassium bromide and 50 parts of potassium iodide in 6,100 parts of water along with 300 parts of gelatin.

In mixing B, the halid salts are first dis- 11 solved, the water and the gelatin then added Solution B is then warmed, say to F. or F. for example; and the silver nitrate solution A is gradually added to it with constant stir- 115 ring. It is preferable to warm solution A before adding it to B, say to 150 F. or

F. for instance. When solution A has been thoroughly incorporated in solution B, there are then added 43 parts of strong ammonia previously dissolved in 900 parts of water. The emulsion formed by these operations is allowed to stand for a short time, say 15 minutes to a half hour for ex- Then 1050 parts of gelatin are dis- 125 solved in it with thorough mixing. The emulsion is next cooled, such as by keeping in a cool space, until it sets to a firm jelly. The latter is broken up, as by shredding, for instance, and thoroughly washed to remove soluble salts, such as potassium nitrate and any excess potassium halids. The wash water is, of course, cool enough not to melt the pieces ofemulsion jelly. The washed emulsion is next remelted to 100 F. and 1050 parts of water soaked gelatin are thoroughly mixed into it, the temperature then being raised, say between 120 F. and 150 F., for instance, for a short time, say a few mintues. It is then cooled and set. It is of the ammonia or alkaline type of emulsion.

My sensitizing material may be usefully incorporated at any stage of the above described process of preparing the emulsion, even being premixed with solutions A or B or with ammonia or with the gelatin, at the initial stages. It is very convenient to add it to the otherwise complete, melted, emulsion prior to coating on supports at the final stages in the process of preparing the emul -sion. For example, the emulsion is remelted and there is thoroughly mixed into it 25 parts by volume of my sensitizing material (say one of the alcoholic extracts described above) for each 1000 parts by volume of emulsion. Since the actual sensitizing bodies are in the, colloidized solids in such preparation and since such solids total as only a small proportion of said preparation (generally far less than one twenty-fifth) it follows that the actual sen 'sitizing bodies are very useful when added in even less than one art per thousand of emulsion by weight. ften the ratio is less than one n ten-thousand or one in one hundred-thousand. It will be noted that this addition does not substantially dilute the emulsion, being of the order of two per cent.

With its light-sensitiveness increased by my material, the emulsion, being melted to the desired fiowability, is coated on its support, such as" glass, film, paper, etc., in the well known way. It is convenient to control and check the process by coating samples of the emulsion before and after the addition of my sensitizing material, the coated specimens being tried out photographically by any well known sensitometric test, or even by comparative camera exposures on the same subject, under like conditions. Of course, the usual precautions are observed during the emulsion making and coating processes such as the use of non-actinic or safe light, cleanness of vessels and air, etc.

The different gelatins sold for photographic emulsion-making may be used in the example given above, hard ones being very useful. The temperatures given, are, of course, adjusted if the particular gelatin ,employed has physical properties, such as melting and setting points, which deviate considerably from the usual "ones, such ad- .the American Chemical justment being a matter of routine control. Instead, however, of using gelatins which give emulsions of useful but lower sensitiveness even before the addition of my.

sensitizing material, an almost inert gelatin may be employed,-one which forms an emulsion which 1 produces a developable image only after impractically long exposures, and then does not yield an image of desirable density. A gelatin which forms such a nearly inert emulsion may be prepared in the way described under the heading Preparation of ash-free gelatin in pages 1856 and 1859 of the Journal of Society, September, 1922, Vol. XLIV, No. 9, being'part of an article by Sheppard, Sweet, and Benedict on Elasticit of purified gelatin jellies as a function of hydrogen-ion concentration. Emulsions of impractically low light-sensitiveness made by the above described process from such prepared gelatin, are transformed by my sensitizing material into emulsions which give developable images of excellent density after usefull brief exposures. I have, for example, een able to increase the light-sensitiveness of such low sensitive emulsions over twenty times, the

exposures for a given subject being cut to less than one-twentieth of the original one and the'image density being made excellent by a corresponding gain. Usually the percentage increase in ,light-sensitiveness is at least ten times the percentage increase in volume of the emulsion caused by the addition of material producing said increases. Often it is very much more indeed. Increases of the same general order of magnitude are made when my sensitizing material is added in similar proportions to emulsions which are made from normal photographic gelatins or mixtures of such normal gelatins with said almost inert gelatines, and already have useful, but lower initial sensitiveness. Difl'erent ercentages of sensitizer produce correspon ingly different increases. The increases in developing-out emulsionsappear upon -the usual developing, fixing, washing and drying operations.

For testing the power of sensitizing material, an almost inert emulsion made,v as

above described, from said prepared gela emulsions containin my sensitizing material have improved stability or keeping qualities because of the purification of said material.

My sensitizing material may be incorporated into gelatin with which photographic emulsions are to be made. This strengthened gelatin then constitutes a valuable intermediate in emulsion manufacture. For example, the gelatin can be melted and 10 to 25 parts by volume of my above described aqueous sensitizing material can be thoroughly mixed into 1000 parts of gelatin. Emulsions made from the mixture have increased li ht-sensitiveness as compared with those made from corresponding unstrengthened gelatin. The proportion of sensitizing material is, of course, adjusted to give the desired control of the sensitiveness of emulsions made from thegelatin, the. total sensitizing material in the strengthened gelatin being thus brought above normal. It is especially effective when used in making emulsions having a slight alkalinity.

In the examples given above 'the steps of treating with ammonia and warming of the emulsion j ust; before its final setting improve the photographic properties of the emulsion, es ecially when the latter is made from hard ge atins. But one or both of them may be'i omitteda In other words, my sensitizing material acts by itself to increase the lightsensitiveness, whether ripening steps be employed or not, and so can whollfy or partially replace them. The effect 0 either or both of such steps, however, is to help in crease the light-sensitiveness of the emulsions and thus give a stronger initial sensitized condition which is multiplied or increased by using my sensitizing material. When using the ash-free gelatin mentioned above, they are especially readily dispensed with; but if retained in making very sensitive emulsions, they can be shortened and made more certain in eifect by reason of the use of my powerful and dependable sensitizing material. I consider the materials containing said compounds to be concentrated when they give a useful sensitizing ef-. fect without harmfully diluting the emulsions. My materials do not act as a photographic developer.

. I have described gelatin emulsions because at the present time they are the ones which have the widest practical use. Moreover they form the best medium for testing my sensitizing materials, the characteristic action of such materials on such emulsions being one of the best identifying criteria of such sensitizing materials. Other organic colloids and mixtures of them with" each other or with gelatin, where their nature arabic, cellulosic derivatives such as collodion are instanced. While I have disclosed the use of my sensitizer in connection with such sensitive substances as silver bromide,

and silver iodide, other light-sensitivesubstances can be employed, such as silver chlorid, alone or mixed with one or more of the others.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A biochemical sensitizing material tino-silver-halid emulsions, when incorporated therein, said material comprising a sterol-containing fraction of a biochemical extract, said fraction being in solution in an organic solvent which is without injurious effect on said emulsions.

4. A. photographic sensitizing material comprising a sterol-containing. fraction of a biochemical extractdissolved in alcohol and having the Property of increasing the lightsensitiveness of gelatino-silver-halid emulsions when incorporated therein.

5. A biochemical photographic sensitizing extract which has the property of increasing the general light-sensitiveness of developingout photographic gelatino-silver-halid emulsions of the alkaline type without altering the grain-size characteristics thereof, said material being substantially free from its normally associated alcohol-insoluble biochemical substances.

6. A biochemical photographic sensitizing material which is substantialy all soluble in alcohol and has the property of increasing by itself, the general light-sensitive'ness of photographic gelatin'o-silver-halid emulsions, without substantially altering. the grain-size characteristics thereof.

7. A sensitizing material in concentrated form which has the property of increasing the general light-sensitiveness of photo-- graphic gelatino-silver-halid emulsions without increasing the grain-size thereof, said material comprising a sterol-containing fraction of abiochemical extract, said fraction being in an organic solvent which is without iniurious effect on said emulsions and is miscible with water.

having the property of increasing the general light-sensitiveness of photographicgelatino-silver-halid emulsions without increasing the grain-size thereof. H

9. A photographic sensitizing material which has the property, even in the absence of dye and inorganic sensitizers, of increasing the light-sensitiveness of photographic gelatino-silver-halid emulsions when incor porated therein, said material comprising a sterol-containing fraction of a biochemical extract, said fraction bein in a volatile organic solvent which is without injurious effect on said emulsions.

10. In the process of preparing from a mixture containing associated bulky impurities, a biochemical sensitizing material which has the property of increasin the general light-sensitiveness of gelatino-sllverhalid photographic emulsions, the step of extracting said material away from at least part of said bulky associated impurities with 1 an organic solvent of said material.

11. In the process of preparing, from a mixture containing lmpurlties insoluble in ligroin, a biochemical purified sensitizing material which has the property of increasing the general light-sensitiveness of photographic emulsions when incorporated therein, the step of extracting said material from said mixture with .ligroin.

12. In the process of preparing,from a liquid carrying the same, a purified biochemical sensitlzing material which has the property of increasin the light-sensitiveness of gelatino-silver-halid emulsions when incorporated therein, precipitating said material with impurities from said liquid, and separating said material from said impurities.

. 13. In the process of preparing a purified biochemical sensitizing material which has the property of increasing the light-sensitiveness of photographic gelatino-silverhalid emulsions in which it is incorporated, the steps of taking up said material in a liquid vehicle, forming a precipitate of'nonsensitizing substance in said liquid which carries with it said sensitizing material, and extracting said sensitizing material from said precipitate.

14. In the process of preparing a purified biochemical sensitizing material which has the property of increasing the light-sensitiveness of photographic gelatino-silver halid emulsions when incorporated therein, the steps of forming an aqueous extract containing said sensitizing material, forming in said extract a precipitate to which said material becomes attached, collecting said precipitate and dissolving said material from said precipitate with an organic solvent.

15. In the process of preparing a purified biochemical sensitizing material which has the property ofincreasing the light-sensitiveness of photographic gelatino-silver halid emulsions when incorporated therein, the steps of forming an aqueous extract containing said material from a gelatin-source, forming in said extract a precipitate to which said material becomes attached, separating said precipitate and extracting said material from the precipitate with an organic solvent. 7

16. In the process of preparing, from a mixture containing impurities, a biochemical sensitizing material which has the property of increasing the general light-sensitivencss of a gelatino-silver-halid emulsion in which it is incorporated, the steps of extracting said material from said mixture with an organic liquid and concentrating the extract.

17. Inthe process of preparing, from a de'iming solution, a sensitizing material which has the property of increasing the light-sensitiveness of photographic gelatinosilver-halid emulsions when incorporated therein, the steps of forming in said deliming solution a precipitate to which said material becomes attached, separating said precipitate, and dissolving said material from said precipitate.

18. In the process of preparing, from a deliming solution containing a coagulable substance, a sensitizing material which has the property of increasing the light-sensitiveness of photographic, gelatino-silvcrhalid emulsions when incorporated therein, the steps of coagulating said substance to entrap said material in the coagulated precipitate thus formed, separating said pre cipitate, and extracting said material from said, precipitate.

19. In the process of preparing, from a deliming. solution containing coagulable albuminous substances, a sensitizing'material which has the property of increasing the light-sensitiveness of photographic gelatino silver-halid emulsions when incorporated therein, the steps of coagulating said albumins, collecting the coagulum, and extracting said material from the coagulum.

20. In the process 0t preparing, from a mixture which includes a sterol and impurities, a sensitizing .material which has the property of increasing the light-sensitiveness of photographic gelatino-siiver-halid emulsions when incorporated therein, the steps of altering the solubility of said impurities and extracting a sterol fraction with a solvent in which said altered'impurities are substantially insoluble.

21. In the process of preparing, from av mixture which includes impurities, a sensitizing material which has the property of increasing the light-sensitiveness of photographic gelatino-silver-halid emulsions when incorporated therein, the steps of extracting said material from said mixture in an organic liquid and then evaporating said extract down to substantial dryness.

22. In the process of preparing, from biochemcial tissues containing the same, a sensitizing material which has the property of M increasing the light-sensitiveness of photographic gelatino-silver-halid emulsions when incorporated therein, the steps of extractlng said material from the bulk of said tissuebut in a form mixed with minor impurities, altering the solubility of said impurities, and dissolving said material from said altered impurities with a solvent in which said impurities are substantially insoluble.

23. In the process of preparing, from grain tissue containing the same, a sensitizing.materi al which has the property of increasing the light-sensitiveness of photographic gelatino-silver-halid emulsions when incorporated therein, the steps of extracting said material from the bulk of'said tissues but in a form containing minor saponifiable impurities, saponifying said impurities, and separating said material from said saponilied impurities.

24:. A photographic emulsion comprising a colloid, particles of photographic compound suspended therein, and an independent biochemical sensitizing extract therein upon which at least part of the general light-sew sitiveness of said emulsion depends, said extract being substantially all soluble in alco- 1101.

25. A photographic gelatino-silver-halid emulsion of relatively high light-sensitive ness substantially free from dye-sensitizers, comprising amixture of the constituents of a gelatino-silver-halid emulsion of lower light-sensitiveness and an independent biochemical sensitizing materialupon which depends the difierence between said lower and said high light-sensitiveness, said material being substantially free from its alcohol-insoluble impurities.

A 26. A photographic gelatino-silver-halid emulsion of relatively high light-sensitiveness comprising a mixture of the constituents of a gelatino-silver-halid, emulsion of lower light-sensitiveness and a sterol extract containing a sensitizing material upon which,

independent of dye, depends the difference between said lower and said high light-sensitiveness, said extract being soluble in an organic solvent which is substantially free from injurious effect on said emulsions.

27. A photographic developing-out gela: tino-silver-halid emulsion of relatively high light-sensitiveness comprising a mixture of the constituents of a gelatino-silver-halid emulsion, having certain grain-size characteristics and lower light-sensitiveness and an independent sensitizing material upon which depends the difference between said lower and said high light-sensitiveness, said material being substantially without effect on said grain-size characteristics and comprising a sterol extract soluble in an organic solvent which is substantially free from injurious effect on said emulsions.

28. A photographic developing-out gelatino-silver-halid emulsion of the alkaline. type comprising the constituents of. a gelatino-silver-halid emulsion of lower lightsensitiveness and an independent biochemical sensitizing material comprising a sterol fraction in alcohol, upon which material the difference between said lower and said higher light-sensitiveness depends, irrespective of the action of a dye.

29. A photographic gelatino-silver-halid emulsion substantially free from dye sensitizers havin characteristics of manufacturing standar comprising the constituents of a developing-out gelatino-silver-halid emulsion of sub-standard general light-sensitiveness but otherwise of standard characteristics and an independent biochemical sensitizing extract, substantially free from its originally associated alcohol-soluble impurities upon which the difference between said sub-standard andstandard general light-sensitiveness depends, the other characteristics beingsubstantially independent of said extract.

30. A photographic gelatino-silver-halid emulsion having light-sensitiveness over a definite spectral range, said emulsion comprising a mixture of the constituents of a gelatino-silver-halid emulsion of relatively lower light sensitiveness over said range, and a biochemical sensitizing material, substantially free from its originally associated alcohol-insoluble impurities, upon which material alone depends the difterence between said first and second named light-sensitiveness over said range.

31. A photographic gelatino-silver-halid emulsion having light-sensitiveness over a definite spectral range and having definite grain-size characteristics, said emulsion comprising the constituents of a gelatino-silverhalid emulsion having substantially the same definite grain-size characteristics but having a relatively lower light-sensitiveness over said spectral range, and a sensitizing material upon which depends the difference in light-sensitiveness between the first and second named emulsions over said spectral range, the grain-size characteristics being substantially independent of said sensitizing material, the latter comprising a sterol extract in an organic solvent which is without injurious effect on said emulsion.

32. A photographic colloid-silver-halid emulsion comprising a colloid. silver halid particles suspended therein and a biochemi- 130 cal sensitizing material upon which at least part of the general light-sensitiveness said emulsion depends, the ratio of said material to said silver-halid being substantiall inde endent of the ratio of said COllOld to said silver-halid, said material being substantially free from its originally associated alcohol soluble impurities.

33. A photo raphic developing-out gelatino-silver-hali tin, silver halid particles suspended therein and a biochemical sensitizing material upon which a large part of the general lightsensitiveness of said emulsion depends, the ratio of gelatin to silver-halid being substantially unaffected by said material, and

the latter comprising a sterol extract in an organic solvent which is substantially inert toward said emulsion.

34. A photographic 'gelatino-silver-halid emulsion comprising a suspension in gelatin of silver halid particles and an independent biochemical sensitizing extract substantially free from its originally associated alcoholinsoluble impurities, the percentage of general li ht-sensitiveness of said emulsion due to sai extract being greater than the percentage of the total volume taken up by said extract.

35. A photographic gelatino silver-halid emulsion comprising a mixture of gelatin, silver halid particles, and a sensitizing sterol extract in a solvent which is substantially inert toward said emulsion, the percentage of light-sensitiveness of said emulsion due to said extract being much greater than the percentage of it by volume in said mixture, and being substantially independent of dye.

36. A photographic emulsion comprising a suspension mixture of gelatin, silver halid particles, and an independent sensitizing material containing a sterol extract in an,.

organic solvent which is inert toward said emulsion, the proportion of light-sensitiveness due to said material being greater than the order of 2 per cent, when the proportion byvolume of said material does not exceed the order of 2 per cent.

37. A photographic emulsion comprising a suspension mixture of gelatin, silver halid particles, and a concentrated biochemical sensitizer substantially free from its originally associated alcohol-insoluble impuri ties, the proportion of the general lightsensitiveness of said emulsion due to said material independent of dye being at least 10 times the proportion of said material by volume.

38. A photographic emulsion comprising a suspension mixture of gelatin, silver halid 7 particles, and a concentrated sensitizing sterol extract, the proportiomof the lightsensitiveness of said emulsion due to said extract being at least of the order of 20 per cent'or more when the proportion by emulsion comprising gelavolume of said extract does not exceed the order of 2 per cent.

39. In the process of preparing a hotographic emulsion, incorporating t erein sufficient biochemical sensitizing extract, substantiall free from its originally associated alco ol-insoluble im urities, to increase the general light-sensitiveness of said emulsion.

40. In the process of preparing a colloidr sensitive-silver-salt emulsion, incorporating with the other constituents thereof sufficient sensitizing sterol extract to increase the light-sensitiveness of said emulsion, said extract being soluble in an organic solvent which is substantially harmless to said emulsion.

41. In the process of preparing a colloidsensitive-silver-salt emulsion substantiall free from dye sensitizers, incorporating wit the other constituents thereof a sensitizing sterol extract, soluble in the general light-sensitiveness of said emulsion.

42. In the process of preparing a photographic gelatino-silver-halid emulsion of relatively high general light-sensitiveness, and substantially free from dye sensitizers, combining with the constituents of a gelatinosilver-halid emulsion of lower light-sensitiveness, sufiicient biochemical sensitizing material, substantially free from its originally associated alcohol-insoluble impurities, to cause said high general light-sensitiveness.

43. In the process of preparing a photographic gelatino-silver-halid emulsion, in corporating with the other constituents thereof enough concentrated sensitizing material, substantially free from its original- 1y associated alcohol-insoluble impurities, to increase the general light-sensitiveness of said emulsion independently of dyes without acting to increase the grain-size thereof.

44. In the process of preparing a photographic developing-out gelatino-silver-halid emulsion of the alkaline type, incorporating with the other constituents thereof sutlicient biochemical sensitizing material, substantially free from its originally associated alcohol-insoluble impurities, to increase the light-sensitiveness thereof, irrespective of the action of dye and inorganic sensitizers.

45. In the process of preparing a photographic 'gelatino-silver-halid emulsion, incorporating with the other constituents thereof suflicient concentrated sensitizing sterol extract, in an organic solvent which is substantially free from injurious action on said emulsion, to increase the light-sensitivene'ss thereof irrespective of dye and inorganic sensitizers.

46. In the process of preparing a photographic colloid-sensitive-silver-salt emulsion, increasing .the general light-sensitiveness,

alcohol to increase without substantially altering the ratio of colloid to silver salt, by incorporating in said emulsion sufiicient biochemical sensitizing extract, substantially free from its ori inall associated alcohol-insoluble colloi s, to e ect said increase.

47. In the process of preparing a photographic gelatino-silver-halid emulsion, increasing the general light-sensitivness thereof more than 2 per cent by addin thereto less than 2 per cent by volume of a iochcmical sensitizing material, substantially free from its originally associated alcohol-insoluble impurities and having active sensitizing bodies therein more highly concentrated than those in the emulsion treated.

48. In the process of preparing a developing-out photographic gelatino-silver-halid emulsion, increasing the general light-sensitiveness thereof through a percentage at least ten times greater than the corres ond ing percentage increase in volume 0 said emulsion by incorporating therein a sufiiciently concentrated sensitizing sterol extract, soluble in an organic solvent that is substantially inert toward said emulsion.

49. In the process of making a photographic colloid-sensitive-silver-salt emulsion separating from its alcohol-insoluble associated impurities a biochemical sensitizing extract and incorporating suflicient of said material in preparing ,said emulsion to increase the general light-sensitiveness thereof.

50. In the process of m'aking a photographic gelatino-sensitive-silver-salt emulsion, substantially free from dye sensitizers, separating from at least part of its normally associated alcohol-insoluble impurities a sonsitizing sterol extract and incorporating it with other constituents in preparing said emulsion. I

51. In the process of making a developingout photographic colloid-sensitive-silvcrsalt emulsion, separating a sensitizing material from a mixture thereof with impurities by means of an organic solvent, and incorporating sufficient of said material in said emulsion to increase the general light-sensitiveness thereof.

52. In the process of making a developingout photographic gelatino-silver-halid emulsion of the alkaline type, dissolving a biochemical sensitizing material from a mixture thereof with impurities by means of an organic solvent in which said material is more soluble than said impurities and which is substantially without injurious action on said emulsion, and incorporating sufiicient of said material, in solution in said solvent,

into said emulsion to increase the general light-sensitiveness thereofx 53. In the process of making a photographic gelatino-silver-halid emulsion, extractinga biochemical sensitizing material from its associated impurities with alcohol,

and incorporating suflicient of the extracted material with the constituents of said emulsion to increase the general light-sensitiveness of the latter.

54. In the process. of making a photographic gelatino-silver-halid emulsion, precipitating from a liquid carrying the same a biochemical sensitizing material, andincorporating said material with the constituents of said emulsion to increase the lightsensitiveness thereof.

55. In the process of making a photographic gelatino-silver-halid emulsion, pre cipitating from a liquid carrying the same a biochemical sensitizing material, extracting said material from said precipitate and incorporating sufiicient of said extracted material with constituents of said emulsion to increase the light-sensitiveness of the latter.

56-. In the process of making a photographic gelatino-silver-halid emulsion, forming in a liquid which carries biochemical sensitizing material a precipitate to which said material adheres, separating said material from said precipitate and incorporating suflicient of said material in said emulsion to increase the light-sensitiveness thereof.

57. In the process of making a photo graphic gelatino-silver-halid emulsion, taking up in a liquid vehicle a biochemical sensitlzing material, forming in said liquid vehicle a precipitate which carries'said material with it, extracting said material from 'said precipitate, and incorporating said material with the constituents of said emulsion to increase the light-sensitiveness thereof.

58. In the process of making a photographic gelatino-silver-halid emulsion, taking up in one liquid a biochemical sensitizing material, separating said material into a different liquid, and incorporating said material in said emulsion.

' 59. In the process of making a photographic gelatino-silver-halid emulsion, extracting a biochemical sensitizing material from impurities with one liquid, separating said material from said liquid, dissolving said material in a different liquid which is substantially without injurious action on said emulsion, and incorporating sufficient of said solution in said emulsion to increase the light-sensitiveness thereof.

60. In the process of making a gelatinosilver-halid emulsion, taking up inan aqueous liquid a biochemical sensitizing material, forming in said liquid a precipitate to which said material adheres, collecting said precipitate, dissolving said material from said precipitate, and incorporating suflicient of said material with the constituents of said emulsion 'to increase the light-sensitiveness thereof. 3

61. In the process of making a photographic gelatino-silver-halid emulsion, ex-

tracting from a gelatin source into an.

aqueous liquid a sensitizin material'and a coagulable albumin,- coagu ating said albumin to collectsaid material in the coagulum, separating said material from the coagulum, and incorporating suflicient of said material in said emulsion to increase the light-sensitiveness thereof,

62. In the process of making aphotographic gelatino-silver-halid emulsion, heating a deliming solution to produce a coagulum, extracting from the latter a sensitizing material, and incorporating said material in said emulsion.

63. In the process of making a photographic gelatino-silver-halid emulsion, extracting from a gelatin source into an aqueous liquid a sensitizing material, forming in said liquid an inorganic precipitate to which said material adheres, separating said matei ial from the precipitate, and incorporating said material with the ingredients of said emulsion to increase the lightsensitiveness thereof.

64:- In the process of making a photographic gelatino-silver halid emulsion, precipitating aluminum hydroxide in a deliming solution extracting from said precipitate a sensitizing material, and incorporating said material in said emulsion.

65. In the process of making a photographic emulsion, extracting biochemical sensitizing material from impurities with an organic solvent which is substantially harmless toward said emulsion, concentrating said extract, and incorporating said extract in said emulsion 1n a proportion less than 2 per cent by-volume of said emulsion,

said concentrating of the extract being so high that said incorporated extract increases the light-sensitiveness of said emulsion more than 2 per cent.

66. In the process of making a photographic emulsion, extracting a sensitizing sterol fraction from impurities, concentrating it, and incorporating at least part of the concentrated fraction in said emulsion, the concentrating being carried to a point where the incorporated concentrated extract increases the light-sensitiveness of said emulsion in a larger proportion than it increases the volume of said emulsion.-

67. In the process of making a photographic gelatino-silver-halid emulsion, extracting a sensitizing material substantially free from alcohol-insoluble impurities from an impure mixture containing the same, concentrating the extract, and incorporating said extract in said emulsion, said concentrating being carried to a point where the concentrated incorporated extract increases the light-sensitiveness of said emulsion by a percentage more than 10 times as great as the percentage through which it increases the volume of the emulsion.

light-sensit1veness than those 68. An intermediate for use in making photographic emulsions comprisin an emulsion-forming colloid and an in ependent bio-chemical sensitizingmaterial incorporated therein, said material being substantially free from its originally associated alcohol-insoluble impurities, said intermediate having the property of forming emulsions of higher light-'sensitiveness than those formed under parallel conditions from said colloid without said material.

69. An intermediate for use in the making of photographic emulsions comprising an emulsion-forming colloid and a sensitizing sterol extract incorporated therein, said extract being substantially free from its originally associated alcohol-insoluble impurities, said intermediate having the property of forming emulsions of hi her general I Formed under parallel conditions from said colloid without said extract.

70. An intermediate in the manufacture of photographic gelatino-silver-halid emulsions, comprising gelatine and an independent biochemical sensitizing material incorporated therein, said material being substantially free from its alcohol-insoluble originally associated impurities said intermediate having the property of forming emulsions of higher general light-sensitiveness than those formed under parallel conditions from said gelatin without said material.

71. An intermediate in the manufacture of photographic gelatino-silver-halid emulsions, comprising gelatin, and an independent sensitizing sterol extract soluble in alcohol incorporated therein, said intermediate having the property of forming emulsions of higher general light-sensitiveness than those formed under parallel conditions from said gelatin without said extract.

72. An intermediate for forming photographic gelatino-silver-halid emulsions, com prising a mixture of gelatin and an independent biochemical sensitizing material substantially free from its originally associated alcohol-insoluble impurities, said intermediate having the property of forming gelatino-silver-halid emulsions of higher light-sensitiveness but substantially the same grain-size characteristics as those formed under parallel conditions from said gelatin without said material.

73. An intermediate for forming photographic gelatino-silver-halid emulsions, comprising a mixture of gelatin and a sensitizing sterol extract soluble in an organic solvent, said intermediate having the property of forming gelatino-silver-halid emulsions of higher general light-sensitiveness but sub stantially the same grain-size characteristics as those formed under parallel conditions from said gelatin without said material. 1

74. In the process of preparing an intermediate for the manufacture of photographic emulsions, the step of incorporating in an emulsion-forming colloid a biochemical sensitizing material substantially free from its originally associated alcohol-insoluble impurities and capable of increasing the light-sensitiveness of said emulsions.

75. In the process of preparing an inter- 

